AN EARLY MIOCENE TRANSITION IN DEFORMATION REGIME WITHIN THE RED RIVER FAULT ZONE, YUNNAN, AND ITS SIGNIFICANCE FOR INDO-ASIAN TECTONICS
AN EARLY MIOCENE TRANSITION IN DEFORMATION REGIME WITHIN THE RED RIVER FAULT ZONE, YUNNAN, AND ITS SIGNIFICANCE FOR INDO-ASIAN TECTONICS
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DOI：
10.1029/92jb00109
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发表时间：
1992-05-10
影响因子：
3.9
通讯作者：
TAPPONNIER, P
中科院分区：
文献类型：
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作者：
HARRISON, TM;WENJI, C;TAPPONNIER, P
最近的研究倾向于支持这样一种观点，即印度支那沿着红河断裂带的侧向挤压是容纳印度与亚洲会聚的一个重要因素。为了更好地理解这一特征的性质和时间，对云南南部哀牢山/红河变质带中的矿物进行了40 Ar/39 Ar年龄谱分析。用扩散域理论解释，这些结果产生在550-150 ℃温度范围内的热历史。从这些结果中观察到的冷却速率的不连续性表明，在早中新世在剪切带变形风格的过渡。至少在我们的样品附近，左旋，走滑韧性变形似乎已经停止了约20马。剪切带中的糜棱岩片麻岩随后斜向无顶，可能是由于沿剪切带东部边缘的正断层沿着的一部分，造成了短暂的（局部< 1百万年）但快速（> 100 ℃/百万年）冷却期这种转变可能是由于东北-西南伸展的一个组成部分，该组成部分可归因于大约20 Ma后印度支那相对于华南的顺时针旋转，而不是与沿断层的纯走滑沿着。哀牢山-点苍山正断层泥粘土矿物K-Ar年龄在20 ~ 185 Ma之间，但在20-25 Ma之间有明显的聚集现象。这些结果表明，早中新世哀牢山山前正断层的前兆运动导致了剪切带的斜向去顶。这一早中新世事件在时间上与整个喜马拉雅山和西藏南部从低到非常高的剥蚀率的过渡相对应。这种巧合可能反映了一旦红河断裂带的左旋走滑运动减缓或终止，印度大部分持续向北汇聚的容纳发生在主中央冲断带上，导致特提斯喜马拉雅和冈底斯带的快速隆升。
Recent work has tended to support the view that lateral extrusion of Indochina along the Red River fault zone was a significant factor in accommodating the convergence of India with Asia. To better understand the nature and timing of this feature, 40Ar/39Ar age spectrum analyses were undertaken on minerals from the Ailao Shan/Red River metamorphic belt in southern Yunnan, China. Interpreted using diffusion domain theory, these results yield thermal histories in the temperature range 550-150-degrees-C. Discontinuities in cooling rates observed from these results suggest a transition in deformation style in the shear zone during the early Miocene. At least in the vicinity of our samples, left-lateral, strike-slip ductile deformation appears to have ceased by about 20 Ma. The mylonitic gneisses in the shear zone were subsequently obliquely unroofed, probably due to a component of normal faulting along the eastern edge of the shear zone causing a brief (locally < 1 m.y.) but rapid (> 100-degrees-C/m.y.) cooling episode. This transition may have resulted from a component of northeast-southwest extension attributable to greater clockwise rotation of Indochina relative to South China after approximately 20 Ma than that consistent with pure strike-slip along the fault. K-Ar ages on clay minerals from gouge within the normal faults bounding the Ailao Shan and Diancang Shan yield a range of ages between 20 and 185 Ma but show a significant clustering at 20-25 Ma. These results suggest that early Miocene movement on a precursor to the Range Front normal fault in the Ailao Shan caused oblique unroofing of the shear zone. This early Miocene event corresponds in time with a transition from low to very high denudation rates throughout the Himalaya and southern Tibet. This coincidence may reflect that once left-lateral strike-slip motion on the Red River fault zone slowed or was terminated, accommodation of much of the continued northward convergence of India occurred on the Main Central Thrust resulting in rapid uplift in the Tethyan Himalaya and Gangdese belt.